1. Field of the Invention
The present invention relates to a steam trap for automatically discharging condensate generated in various kinds of steam using equipment and steam pipe lines, and, more particularly, to a thermally-actuated steam trap adapted to discharge the condensate below a desired temperature out of a system by using a temperature control element including a medium which is heated and expanded by steam and cooled and contracted by condensate.
2. Description of the Prior Art
The temperature control element used for a steam trap comprises two disk-like wall members and a diaphragm member provided between the wall members, the diaphragm member being secured at its outer peripheral edge to both the wall members, and the inner space formed thereby accommodating an expansible medium which changes in volume corresponding to the temperature of the fluid which comes into contact with the medium through the diaphragm member. Further, a valve member which cooperates with a valve seat member is carried on the diaphragm member at the side opposite to the expansible medium side.
In the steam trap provided with such a temperature control element, the temperature control element is disposed within a valve chest connected to an inlet, and the valve member carried on the diaphragm member is moved utilizing the expansion and contraction of the expansible medium to thereby bring the valve member into and out of seating engagement with the valve seat member having a discharge passage communicating with the valve chest and an outlet.
When the steam trap is closed, the inner pressure generated by the expansible medium within the temperature control element overcomes the tensile force of the diaphragm to cause the diaphragm to be deflected. This inner pressure depends upon the temperature and working pressure of the condensate to be discharged or of the steam not to be discharged, as is widely known.
Various proposals have hitherto been made to attach the valve member to the diaphragm member.
For example, U.S. Pat. No. 3,698,633 (corresponding to DE P2038344 or JP-B-Sho 51-21174 (1976)) discloses the fact that the valve member is welded to the diaphragm member at the annular jointing portion which encloses the periphery in the vicinity of a central plug, and the diaphragm member encloses the annular jointing portion concentrically and is provided in a stretched manner between the clamping surfaces of the valve member and holding plate provided in opposite relation to each other.
In this prior art, the diaphragm and the valve member are evenly welded at their flat central portions with each other by a central annular seam. Moreover, the diaphragm is held at the outer annular portion between the valve member and the holding plate. To this end, caulking of the holding plate and the valve member is performed.
In order to avoid such a caulking operation and further avoid a situation in which expansion and contraction of the diaphragm, when welded, reach up to the region where movement of strokes of the diaphragm is performed, thereby causing deformation or residual stress in the region, U.S. Pat. No. 4,161,278 (corresponding to DE-P2630038 and JP-B-Sho 60-46318 (1985)) discloses the fact that the edge portions of the diaphragm sheet and holding plate adjacent to the central openings are formed so as to correspond to the outer peripheral surface of the central annular raised portion of the valve member, and the valve member, the diaphragm sheet and the holding plate are welded and sealed with each other at the above-mentioned edge of the annular raised portion.
However, with such a welding manner, it is difficult to hold the valve member, diaphragm sheet and holding plate in their welding positions without any clearances left therebetween, because in welding, after the inner peripheral edge of the diaphragm sheet is aligned to the outer peripheral surface of the raised portion of the valve member, the holding plate is placed thereon and then the welding is performed while pressing the holding plate thereto, thus causing the edges of the holding plate and diaphragm sheet to be apt to float. This impairs the condition of intimate contact between the ends of the members, causing faulty welding. If the wall of the holding plate is thickened, such a floating of the edge portions can be considerably improved, however, in such a case, the,holding plate exists in the space where the expansible medium for the temperature control element is accommodated, and the space requires a given volume or a greater volume for accommodating the expansible medium, thereby resulting in a temperature control element greater in size. In addition, when it is attempted to align the inner peripheral edge of the thin diaphragm sheet with the outer peripheral surface of the raised portion of the valve member, the end of the sheet is subjected to a force which pulls the sheet outwardly, so that it is difficult for the inner peripheral edge of the sheet to come closely into contact with the outer peripheral surface of the annular raised portion over the entire periphery.
Moreover, German patent No. 3124459 (DE 3124459 C2) discloses the fact that the diaphragm and fastening plate, each having a hole in the center thereof, and the side of the valve member directed toward the diaphragm and having an undercut blind hole are welded with each other at their inner peripheral edges. However, with such a practice, precisely aligning the edge of the diaphragm with the portion to be welded is difficult, and some influence due to expansion and contraction of the diaphragm when welded can not be prevented from being exerted on the region where movement of strokes of the diaphragm is performed.